As described in the aforementioned copending application (see also German patent document No. 3,119,332), the railroad bogie, undercarriage or truck can have to or more sets of wheels mounted in a support frame which can pivot about a vertical or upright axis relative to the chassis of the railroad vehicle to enable the latter to successfully negotiate curves or the like.
In driving carriages of this type, one or more drive motors, especially electric motors, are fixed to the undercarriage and connected by universal joint shafts to the driven axle to propel the wheels.
Such railway undercarriages are widely used and, for example, are incorporated in the E120 electric locomotives of the German Federal railway system. To minimize the mass which is not resiliently suspended, the drive unit of such trucks is generally pivotally mounted in the wheel-carrying frame utilizing pivots whose axes run perpendicular to the direction of the vehicle travel.
While this system has been largely effective, in recent years there has been an increasing interest in higher capacity rail systems, higher speed railroad trains and vehicles capable of carrying larger loads at these higher speeds.
As these demands have increased, the sensitivity to masses which were not resiliently suspended or adequately suspended relative to the vehicle bodies has increased. Special spring systems were proposed for the drive unit and the respective transmission, both of which are comparatively heavy.
Such special suspension arrangements were not only complicated and expensive but also required considerable maintenance and were prone to failure.